The present invention relates generally to wire-grid polarizers for the visible and near visible spectrum.
A wire grid polarizer (WGP) is an array of parallel wires disposed on the surface of a substrate, such as glass. Usually wire-grid polarizers are a single, periodic array of wires on the substrate. The grid acts as a diffraction grating when the period of the wires is greater than about half of the wavelength of light. The grid acts as a polarizer when the period of the wires is less than about half the wavelength of light.
While it is desirable for a WGP to transmit all of the light of one polarization and reflect all of the other polarization, no polarizer is perfect. Real WGPs will transmit some of the light of both polarizations and will reflect some of the light of both polarizations. When light is incident on the surface of a transparent material, such as a sheet of glass, a small amount of the light is reflected. For example, at normal incidence, about 4% of the incident light is reflected from each surface of the glass.
It has been suggested to dispose a film under a WGP, or between the wires and the substrate, to move the first diffraction order to shorter wavelengths in order to improve performance in part of the visible spectrum, such as blue light. See U.S. Pat. No. 6,122,103. The film has an index of refraction less than that of the substrate. It has also been suggested to etch into either the substrate or underlying layer to further reduce the effective refractive index under the wire grid. See U.S. Pat. No. 6,122,103. It has been further suggested to form each wire as a composite with alternating metal and dielectric layers. See U.S. Pat. No. 6,532,111.